Looking for military patch

Long story short, I'm doing some research on husband's grandfather M, who was killed in WW2 when his ship was shelled at Iwo Jima. During the course of my research, I found a man who was on the ship at the same time. He's really helped me a lot and given me things about the ship that I didn't even know existed. We have thought about ways to thank him and one involves a patch from the ship. The only problem is that the ship was decommissioned years ago and I don't know where to find patches from a ship that old. Does anyone have any ideas?